1. Field of the Invention
The present invention generally relates to magnetic recording media used in magnetic recording and reproducing apparatuses, and, more particularly, to a substrate for a magnetic recording medium that can reduce the floating height of the magnetic head in compliance with higher recording densities. The present invention also relates to a method of evaluating a magnetic recording medium that can reduce the floating height of the magnetic head.
2. Description of the Related Art
For a magnetic recording medium, such as a magnetic disk, the substrate is produced by providing nickel-phosphorus plating on the surface of an aluminum alloy, for instance, and polishing the resultant. On the surface of the substrate, irregularities are formed by a texture process. The reason why those irregularities are positively formed on the surface of a magnetic recording medium is that the magnetic head can magnetically record and reproduce information on the magnetic recording medium while maintaining a very small floating height from the magnetic recording medium. In this manner, the magnetic head can be prevented from adhering to the surface of the magnetic recording medium, and the frictional resistance can be reduced.
In recent years, however, there has been an increasing demand for higher-density magnetic recording and reproduction apparatuses, such as magnetic disk devices used in computers. In response to such a demand, it is necessary to reduce the magnetic spacing between the magnetic head and the magnetic disk, i.e., the floating height of the magnetic head, as much as possible. Recently, a glide height value that is the distance from the disk average surface is required to be 10 nm or less, and a head floating height is required to be 30 nm or less.
Japanese Laid-Open Patent Application No. 9-326115 discloses a technique of reducing the head floating height by evaluating the undulations and ripples formed by the irregularities on the surface of a magnetic recording medium.
Also, a magnetic recording medium having a non-texture process performed thereon has been suggested. The non-texture process is performed to restrict the irregularities on the surface within a predetermined range so as to reduce the head floating height. However, the non-texture process cannot solve the problem of head adhesion.
The technique disclosed in Japanese Laid-Open Patent Application No. 9-326115 involves the evaluation of the undulations and ripples in the circumferential direction (the recording and reproducing direction of the magnetic head). In this technique, the floating height of the magnetic head is restricted to 100 nm or smaller. In recent years, however, there has been a demand for magnetic heads having even smaller floating heights, such as 30 nm or less. As a result, it has become difficult to realize such a small floating height only by putting a restriction on the shapes of irregularities in the circumferential direction of the magnetic disk.
Furthermore, in the conventional magnetic disk apparatuses, a contact start stop (CSS) method in which the floating surface of the magnetic head is brought into contact with the surface of a magnetic disk and then slidably moves on the surface of the magnetic disk is widely employed. In order to reduce the floating height, it is necessary to perform the texture process and reduce the heights of the irregularities on the surface of the magnetic disk. However, if the irregularities on the surface of the magnetic disk are made too small in height, the surface of the magnetic disk is smoothed. This will result in the problems of the adhesion and high friction of the magnetic head at the time of contact start and stop.